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`Taming Scattering Amplitudes at Tree Level'

Abstract: We provide a general interpretation and a general
prescription for computing the boundary term arising in the BCFW
construction for on-shell scattering amplitudes at tree level and for
general interactions. It allows us to build any on-shell scattering
amplitude at tree level from a minimal set of hypotheses. This
provides a fully S-matrix, Lagrangian-free, formulation of the tree
level approximation for arbitrary theories in Minkowski space. 
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